The present invention relates to a spray powder including aluminum oxide and titanium dioxide for the manufacture of wear resistant and high temperature resistant coatings, particularly on the running and friction faces of machine parts, such as piston rings, piston bottoms and the fire lands of pistons as well as the friction faces of synchronizing discs, which are subjected to sliding friction and/or high temperature stresses in internal-combustion engines, the powder being preferably applied in a plasma spraying process.
It is known, for example, according to U.S. Pat. No. 3,697,091, to coat the running faces of piston rings for internal combustion engines, instead of with wear resistant hard chromium or molybdenum coatings, with oxide ceramic layers of aluminum oxide and titanium dioxide or zirconium dioxide, preferably in a plasma spray process. Coatings of this type are distinguished by good wear resistance and resistance against burn traces even under high temperature stresses. Such coatings, however, are still relatively sensitive to thermal shocks so that such coatings, be they in chambered or in sprayed-on form, break out (delaminate) and, as a consequence, may produce great wear on their counterrunning partners.
To overcome this problem, DE-PS 3,033,332 and corresponding U.S. Pat. No. 4,248,440 disclose the addition of yttrium oxide in quantities from 2 to 6 weight percent to plasma spray powders which include aluminum oxide and titanium oxide for coatings of piston rings. The resistance of such coatings to thermal shocks has also been significantly improved in this way without substantially reducing wear resistance and high temperature resistance of the coatings. However, these measures have not been able to completely eliminate all of the drawbacks of the aluminum oxide-titanium dioxide plasma sprayed coatings on piston rings, particularly with respect to their resistance to thermal shocks and as a consequence thereof, with respect to their freedom from breakouts and their poor compatibility with their counterrunning partners.